A conventional class-G amplifier needs at least four power supplies, typically referred as VCCH, VCCL, VEEH and VEEL. Two power supplies can also be used with the ground as the negative power rail. However, this would cause a dramatic change of the output common mode voltage when switching supplies, which causes distortion and is not desirable. For higher power efficiency, more power supplies need to be added. This causes higher costs for practical implementation.
A recent development uses a buck converter along with a charge pump to provide adjustable VCC and VEE to reduce the hardware implementation costs and improve the efficiency simultaneously. However, the highest efficiency of the charge pump is nowhere near the buck converter and there is a one-clock cycle latency between the output of the buck converter and the output of the charge pump. In further detail, as shown in FIG. 1, such a class-G amplifier chip 10 uses amplifier circuits 16 and 18 to amplify the audio input signal Vaudio, a buck converter 12 to convert a supply voltage AVDD to a voltage HPVDD for the positive power rail of the amplifier circuits 16 and 18, a charge pump 14 to convert the voltage HPVDD to a voltage HPVSS for the negative power rail of the amplifier circuits 16 and 18, and an audio level detector 20 to detect the audio input signal Vaudio to generate a detection signal for the buck converter 12 to adjust the voltage HPVDD. However, in the class-G amplifier chip 10, a significant difference exists between the highest efficiency of the charge pump 14 and the efficiency of the buck converter 12, and a delay exists between the output HPVDD of the buck converter 12 and the output HPVSS of the charge pump 14, both of which impact the efficiency of the class-G amplifier chip 10. Furthermore, the charge pump 14 requires a flying capacitor Cfly external thereto, in addition to an inductor used by the buck converter, which also increases the hardware costs.
Therefore, it is desired a more efficient and lower cost class-G amplifier.